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A neuron, neurone,  or nerve cell, is an electrically excitable cell that communicates with other cells via specialized connections called synapses.
Neurons are typically classified into three types based on their function.

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A typical neuron consists of a cell body (soma), dendrites, and a single axon. The soma is usually compact. ... The term neurite is used to describe either a dendrite or an axon, particularly when the cell is undifferentiated. Most neurons receive signals via the dendrites and soma and send out signals down the axon.

Cell body: the central part of any cell is the soma, which contains the nucleus being the genetic material (contained in the chromosomes).

Dendrite: Neurons have a large number of extensions called dendrites. Often there are branches or points extending out of the cell body. The surfaces of the dendrites are mainly where chemical messages from other neurons are received.

Axon: Neurons contain an extension that is different from all the other cells, this extension is named as axon. The function of the axon is to transmit an electrochemical signal to other neurons, sometimes at a considerable distance. A neuron´s axon can measure up to one-meter-long, it can go from the spinal cord to the feet.

Myelin; The axons are coated with a layer of myelin, a series of cells that surround the axon (Schwann cells). That makes the axon look like a chain of the sausages, which have a function of covering the electrical impulses (similar to the isolation of electric cables).

Node of Ranvier: Are the spaces between the myelin coating on the neuron's axon. Electricity travels through the axon (wrapped in myelin). In Ranvier's nodes, electricity can be conducted inside the cell, and the electrical signal is propagated by the axon.

Axon terminal: This is where the electrochemical signal that has traveled the length of the axon becomes a chemical message that travels to the next neuron.

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Neurons send signals using action potentials. An action potential is a shift in the neuron’s electric potential caused by the flow of ions in and out of the neural membrane.
Action potentials can trigger both chemical and electrical synapses.

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In a chemical synapse, action potentials affect other neurons via a gap between neurons called a synapse. Synapses consist of a presynaptic ending, a synaptic cleft, and a postsynaptic ending.

When an action potential is generated, it’s carried along the axon to a presynaptic ending. This triggers the release of chemical messengers called neurotransmitters. These molecules cross the synaptic cleft and bind to receptors in the postsynaptic ending of a dendrite.

Neurotransmitters can excite the postsynaptic neuron, causing it to generate an action potential of its own. Alternatively, they can inhibit the postsynaptic neuron, in which case it doesn’t generate an action potential.

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Electrical synapses can only excite. They occur when two neurons are connected via a gap junction. This gap is much smaller than a synapse, and includes ion channels which facilitate the direct transmission of a positive electrical signal. As a result, electrical synapses are much faster than chemical synapses. However, the signal diminishes from one neuron to the next, making them less effective at transmitting.

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Sensory neurons help you:

taste

smell

hear

see

feel things around you

Sensory neurons are triggered by physical and chemical inputs from your environment. Sound, touch, heat, and light are physical inputs. Smell and taste are chemical inputs.

For example, stepping on hot sand activates sensory neurons in the soles of your feet. Those neurons send a message to your brain, which makes you aware of the heat.

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Motor neurons play a role in movement, including voluntary and involuntary movements. These neurons allow the brain and spinal cord to communicate with muscles, organs, and glands all over the body.

There are two types of motor neurons: lower and upper. Lower motor neurons carry signals from the spinal cord to the smooth muscles and the skeletal muscles. Upper motor neurons carry signals between your brain and spinal cord.

When you eat, for instance, lower motor neurons in your spinal cord send signals to the smooth muscles in your esophagus, stomach, and intestines. These muscles contract, which allows food to move through your digestive tract.

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Neurons vary in structure, function, and genetic makeup. Given the sheer number of neurons, there are thousands of different types, much like there are thousands of species of living organisms on Earth.

In terms of function, scientists classify neurons into three broad types: sensory, motor, and interneurons.

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Interneurons are neural intermediaries found in your brain and spinal cord. They’re the most common type of neuron. They pass signals from sensory neurons and other interneurons to motor neurons and other interneurons. Often, they form complex circuits that help you to react to external stimuli.

For instance, when you touch something hot, sensory neurons in your fingertips send a signal to interneurons in your spinal cord. Some interneurons pass the signal on to motor neurons in your hand, which allows you to move your hand away. Other interneurons send a signal to the pain center in your brain, and you experience pain.

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Classification according to the structure of the neuron: 

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Classification according to the structure of the neuron: 

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Multipolar: Multipolar neurons are recognized because they have three or more parts (processes) which extend from the cell body. Multipolar neurons are part of more than 99% of neurons in humans and are the major neuron type found in the Central Nervous System and in the division of the Peripheral Nervous System.

Bipolar: Bipolar neurons have only two parts (processes) that extend in opposite directions from the body of the cell, an element called dendrite and another axon. Although this type of neurons is rare, they are found in the retina of the eye and the olfactory system.

Unipolar: Unipolar neurons have a unique and short part (process) that extends from the cell body and then branches into two more parts (processes) that extend in opposite directions.

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Reflex arc is a neural pathway that controls a reflex. In vertebrates, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord. This allows for faster reflex actions to occur by activating spinal motor neurons without the delay of routing signals through the brain. The brain will receive the sensory input while the reflex is being carried out and the analysis of the signal takes place after the reflex action.

There are two types: autonomic reflex arc (affecting inner organs) and somatic reflex arc (affecting muscles). Autonomic reflexes sometimes involve the spinal cord and some somatic reflexes are mediated more by the brain than the spinal cord.

During a somatic reflex, nerve signals travel along the following pathway:

1. Somatic receptors in the skin, muscles and tendons

2. Afferent nerve fibers carry signals from the somatic receptors to the posterior horn of the spinal cord or to the brainstem

3. An integrating center, the point at which the neurons that compose the gray matter of the spinal cord or brainstem synapse

4. Efferent nerve fibers carry motor nerve signals from the anterior horn to the muscles

5. Effector muscle innervated by the efferent nerve fiber carries out the response.

A reflex arc, then, is the pathway followed by nerves which (a.) carry sensory information from the receptor to the spinal cord, and then (b.) carry the response generated by the spinal cord to effector organs during a reflex action. The pathway taken by the nerve impulse to accomplish a reflex action is called the reflex arc.

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Neurotransmitters are often referred to as the body’s chemical messengers. They are the molecules used by the nervous system to transmit messages between neurons, or from neurons to muscles.

Communication between two neurons happens in the synaptic cleft (the small gap between the synapses of neurons). Here, electrical signals that have travelled along the axon are briefly converted into chemical ones through the release of neurotransmitters, causing a specific response in the receiving neuron.

A neurotransmitter influences a neuron in one of three ways: excitatory, inhibitory or modulatory.